remove wrong assert

this assert didn't prevent anything bad. It was just there to make the code clearer because it was assumed to be true.
The assumption was false so it was removed.

src/persist_var.cpp

@@ -43,7 +43,8 @@ struct persist_choice: mp_sync::user_choice {
 		, side(side_num) {
 	}
 	virtual config query_user(int side_for) const {
-		assert(side == side_for);
+		//side can be different from side_for: if side was null-controlled 
+		//then get_user_choice will use the next non-null-controlled side instead
 		config ret;
 		ret["side"] = side;
 		ret.add_child("variables",ctx.get_var(var_name));